Electrical inverter arrangements

ABSTRACT

An electrical inverter arrangement comprises a polyphase transformer having a delta-connected primary winding and a deltaconnected secondary winding. Positive and negative DC supply lines are provided, and the three junction points of the primary windings are connected to both supply lines through respective electronically controllable switch means. Depending on which switch means are closed, each primary winding can either have 0 volts across it, the full supply volts across it, or half of the full supply volts across it. Each stage of a multistage shift register is connected to control the setting of a respective one of the switch means, and the shift register stages are SET in such order that the resultant operating sequence of the switches causes a substantially sinusoidal variation of voltage across each primary winding, and thus across each secondary winding.

United States Patent Hardie [54] ELECTRICAL INVERTER ARRANGEMENTS [72] Inventor: Neil S. Hardie, London, England [73] Assignee: The Plessey Company Limited, llford, Es-

sex, England [22] Filed: June 15, 1970 [21] Appl. No.: 46,207

[ 51 Jan. 25, 1972 FOREIGN PATENTS OR APPLICATIONS 1,343,999 0/1963 France ..323/27 Primary Examiner-Gerald Goldberg Attorney-Mason, Mason & Albright ABSTRACT An electrical inverter arrangement comprises a polyphase transformer having a delta-connected primary winding and a delta-connected secondary winding. Positive and negative DC supply lines are provided, and the three junction points of the primary windings are connected to both supply lines through respective electronically controllable switch means. Depending on which switch means are closed, each primary winding can either have 0 volts across it, the full supply volts across it, or half of the full supply volts across it. Each stage of a multistage shift register is connected to control the setting of a respective one of the switch means, and the shift register stages are SET in such order that the resultant operating sequence of the switches causes a substantially sinusoidal variation of voltage across each primary winding, and thus across each secondary winding.

7 Claims, 7 Drawing Figures PATENTEDJANZSIHYZ 3.638397 SHEET-10F 3 INVENTOR New. 2;. Akbyg ATTORNEY-S PATENTEDJANZSBYZ 3.638397 INVENTOR NEIL S. HhROIE ORNEY5 l ELECTRICAL INVERTER ARRANGEMENTS A BRIEF SUMMARY OF THE INVENTION The invention relates to electrical inverter arrangements.

According to the invention, there is provided an electrical inverter arrangement comprising a transformer having primary winding means connected to a supply circuit through switch means, the switch means being connected in such a manner as to be selectively operative whereby to provide a plurality of different current paths through the primary winding means, each path providing a different voltage across the same part of the winding means when the supply circuit is energized, thereby varying the voltage induced in secondary winding means of the transformer.

According to the invention, there is also provided an electrical inverter arrangement, comprising winding means, a supply circuit energizable to provide a unidirectional voltage, a plurality of switchable connecting means sequentially settable into a plurality of settings in one of which the winding means is disconnected from the supply circuit and in two further ones of which the winding means is connected to the supply circuit but such as to receive respectively different proportions of the unidirectional voltage from the supply circuit, and control means operative to control the sequence of the settings of the connection means and the duration of each setting such that the resultant voltage variation across the winding means is approximately sinusoidal in shape.

According to the invention, there is further provided an electrical inverter arrangement, comprising a polyphase transformer having a set of polyphase-connected primary windings and a set of polyphase-connected secondary windings, a pair of supply lines, a plurality of switching elements interconnecting the ends of the primary windings to the supply lines, each switch having an ON setting and an OFF setting, and control means connected to control the settings of the switching elements whereby to successively switch the switching elements into each combination of a predetermined sequence ofdifferent switch-setting combinations, the said sequence of switch-setting combinations being such that the voltage variations across the primary windings, when the supply lines are energized by a unidirectional voltage, are mutually phase displaced and vary approximately in the manner of sinusoidal waves.

BRIEF DESCRIPTION OF THE DRAWINGS Electrical inverter arrangements embodying the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

FIG. 1 is a schematic circuit diagram of one electrical inverter arrangement embodying the invention;

FIG. 2 shows waveforms occurring in the arrangement of FIG. I;

FIG. 3 is a more detailed circuit diagram of the arrangement of FIG. 1;

FIG. 4 is a logic diagram of a control ment of FIG. 1; I

FIG. 5 is a logic diagram of a regulation system for use with two arrangements each as shown in FIG. 1;

FIG. 6 shows a schematic circuit diagram of part of another arrangement embodying the invention; and

FIG. 7 is a schematic circuit diagram of a further arrangement embodying the invention.

DETAILED DESCRIPTION The inverter arrangement of FIG. 1 comprises a three-phase transformer having a set 5 of primary windings comprising windings PR, PY, and PB, and a set 6 of secondary windings comprising SR, SY, SB. The primary windings PR, PY, PB are connected, through switches A1, B1, C1, A2, B2, C2 between two supply lines 8 and 10, line 10 being maintained at +V volts relative to line 8.

In a manner to be explained in detail below, the switches are switched ON in a predetermined, repeated, switching system for the arrangesequence so as to energize the primary windings in a corresponding sequence. During this sequence, each primary winding may have 0 volts across it, may have the full voltage +V volts across it, or may share the full voltage +V volts with one other of the primary windings. Thus. for example, if switches A1 and C2 are ON, but all other switches are OFF, then winding PY has the full voltage +V volts across it while each of the windings PR and PB has a voltage V/2 volts across it. If, now, switch B2 is also switched ON then each of windings PR and FY has +volts across it while winding PB has 0 volts across it.

The switching sequence is made up of 12 different switch settings combinations, and these 12 combinations are shown in column 2 of the table below. Column 2 illustrates the switches which are ON for each one of the 12 combinations,

the other switches being OFF. Columns 3, 4 and 5 show the corresponding voltages across the primary windings PR, PY and PB respectively.

Assuming ideal conditions, and a resistive load on the secondary of the transformer, the voltage across each secondary winding SR, SY, SB will be proportional to the voltage across the corresponding primary winding at that time. FIG. 2a therefore, shows the voltage waveform of secondary winding SR, while FIGS. 2b and 2c show the voltages across the secondary windings SY and SB respectively.

FIG. 2 shows that the output waveforms have the same general shape as sine waves and, in fact, require little filtering to approximate very well to sine waves, the first significant harmonic being the fifth (5 percent of which is present).

The harmonic content of the output waveforms can be reduced by using several arrangements each corresponding to the arrangement of FIG. I and adding their output waveforms together at various phase angles; thus, with four arrangements, the fifth and seventh harmonics can be entirely eliminated leaving only the eleventh and higher harmonics. The addition of waveforms can be achieved merely by connecting the secondary windings of the arrangements in series.

FIG. 3 shows a more detailed circuit diagram arrangement of FIG. 1, in which the switches Al to C2 are shown as transistors connected in circuit with six diodes 40.

FIG. 4 shows the logic diagram of a control system for controlling the switching of the transistors of FIG. 4. Each transistor has an associated bistable circuit 42 to 52. When SET, each bistable circuit produces a positive output which is connected to the base of its associated transistor and switches that transistor ON. When RESET, the bistable circuit switches OFF its transistor. The bistable circuits 42 to 52 are controlled by a 12-bit shift register 54 which receives input pulses at a frequency of, in this example, 4,800 per second on a line 56. Each bistable circuit has a SET line 58 and a RESET line 60 and each such control line is connected to a respective one of the stages of the shift register 54. When that stage is in the l state, it energizes the control line connected to it so as to SET or RESET the bistable circuit connected to it according as to whether the control line is a line 58 or a line 60.

The 12 stages of the shift register 54 are numbered to correspond with the numbers given to the 12 combinations of the switching sequence in the table above. Thus, when stage 1 of the shift register is in the l state, it will be seen that bistable circuits 42 and 50 are in the SET state, so as to switch ON the transistors A1 and B2, while all the other bistable circuits are in the RESET state so as to maintain the other transistors OFF. When stage 2 is activated by the next input pulse, bistable circuit 52 is SET, so as to switch ON transistor C2; and so on for the remaining stages of the shift register, in accordance with column 2 of the table.

Instead of using transistors as the switches Al to C2, other suitable devices could be used. For example, silicon-controlled rectifiers could be substituted for the transistors with the addition of suitable commutation circuitry.

The output voltage of inverter arrangements of the type disclosed in FIG. 1 can be regulated in several different ways. In one such way, two inverter arrangements, each as shown in FIG. 1, are used with their secondary windings connected in series to produce the output. Each inverter has a control system generally of the form illustrated in FIG. 4 but modified slightly so as to permit the phase angle of the output of one of the inverter arrangements to be varied relative to that of the other of the inverter arrangements.

Thus, referring to FIG. 5, the first of the two inverter arrangements has a control system comprising a shift register 54, corresponding to the shift register 54 of the system of FIG. 4. This shift register controls the six bistable circuits 42 to 52 (omitted from FIG. for clarity) which in turn control the transistor switches of the inverter arrangement. The shift register 54 of FIG. 5 does not, however, receive its input pulses directly from the input line 56 but receives them through a binary counter 66. The second inverter arrangement is controlled by a shift register 54a which, again, is similar to the shift register 54 of FIG. 4 and controls six bistable circuits (not shown) which, in turn, control the transistor switches of the second inverter arrangement. The shift register 540 receives its pulses from the input line 56 through a binary counter 68.

The shift register 54a and the binary counter 68 are connected to be RESET by means of a line 70 which is energized, through a variable time delay unit 72, from the shift register 54 by means of a line 73. The length of the time delay of the unit 72 is dependent on the value of a control signal applied by a line 74.

In operation, the binary counters 66 and68 are energized by the input pulses on the line 56 and count up in step with the input pulses. When the maximum count of each counter is attained (the maximum counts of the two counters being the same) each counter emits an output pulse which steps its associated shift register so that the latter operates its associated bistable circuits in the manner explained in conjunction with FIG. 4. When each of the l2 stages of the shift register 54 have been activated, line 73 is energized. At the end of the time delay established by the unit 72, line 70 is energized and RESETS the shift register 54a to the state in which its stage 1 is activated and clears the counter 68. Counter 68 then recommences counting the input pulses and steps the shift register 54a. Counter 66 automatically clears itself, and then recommences counting, on attaining its maximum count, and shift register 54 automatically RESETS itself.

If the time delay established by the unit 72 is zero, it will be seen that the two shift registers 54 and 54a will step in phase with each other and thus the output voltages of the secondary windings of the two inverter arrangements will be in phase and will add to produce the maximum voltage output. If, however, the level of the signal on line 74 is adjusted so that a finite time delay is produced by the time delay unit 72, then there will be a difference in phase between the stepping of the shift registers 54 and 54a, and a corresponding difference in phase between the outputs of the two inverter arrangements. The total output voltage will therefore be less. Therefore, the value of the output voltage from the two inverter arrangements can be varied down to 0 merely by varying the level of the signal on the line 74.

The primary windings of the two inverter arrangements can be connected in series as well as their secondary windings, as shown in FIG. 6, and this produces an arrangement particularly suitable for operation with high input voltages. The arrangement of FIG. 6 comprises two inverter arrangements, each similar to that shown in FIG. 1, the primary windings PR, PY, PB of one of the inverter arrangements being connected in series with the primary windings PaR, PaY, and PaB, of the other inverter arrangement, and the secondary windings SR, SY, SB of the one inverter arrangement being connected in series with the secondary windings SaR, SaY, SaB, of the other inverter arrangement. As shown in FIG. 6, six switches A1, B1, C1, A2, B2, C2, corresponding to those as shown in FIG. 1, are provided for controlling the voltages applied across the primary windings but, in addition, a second set of switches Aal, Bal, Cal, Aa2, Ba2, Ca2, are provided. The first set of switches Alto C2 are connected to be controlled by the shift register 54 of FIG. 5 in the manner explained above, while the second set of switches Aal to Ca2 are connected to be controlled by the shift register 54a of FIG. 5. In the manner explained, the'magnitude of the output voltage from the seriesconnected secondary windings can be varied by altering the phase angle between the stepping sequences of the two shift registers. When a high input voltage is applied, however, the switches Aal to Ca2 can all be switched OFF, and maintained OFF (by an automatic protection system if desired) so that the input DC voltage is now applied under control of the first set of switches A1 to C2 alone and is applied across two windings in series instead of across a single winding. Twice the voltage can therefore be sustained without saturating the transformers.

The regulation arrangement described with reference to FIG. 5 or 6 produces a smooth input current, no waveform distortion, and high efficiency. Other regulation arrangements may, however, be used instead and may have particular advantages in certain circumstances. For example, regulation may be achieved by variable pulse-width switching, by regulation of the input voltage, by variation of the waveform shape, or by the use of an auxiliary small regulating inverter.

FIG. 7 illustrates an inverter arrangement which operates in similar fashion to the inverter arrangement of FIG. 1 (items in FIG. 7 corresponding with items in FIG. 1 being similarly referenced) but which has a star-connected winding set as opposed to a delta-connected set. The switches of FIG. 7 are switched ON in a similar sequence to that for the switches of the arrangement of FIG. 1. During this switching sequence, the DC voltage is either applied across two windings in series (with the third winding having 0 volts across it), or across one winding in series with the other two in parallel with each other.

The inverter arrangements described are advantageous in that theswitching devices never have to sustain a higher voltage than the input DC voltage. Little filtering is required to produce high-quality sinusoidal waveforms, and highly unbalanced loads at any phase angle can be supplied. The arrangements permit recirculation of inductive power between phases. In addition, the arrangements are reversible in that the application of alternating current to the output will produce a DC voltage at the input.

What is claimed is:

l..An electrical inverter arrangement, comprising;

electrical winding means;

a supply circuit energizable to produce a unidirectional voltage;

a plurality of switchable connecting means connected between the winding means and the supply circuit and sequentially settable into a plurality of settings in a first one of which the winding means is disconnected from the supply circuit, in second and third ones of which the winding means is connected to the supply circuit but such as to receive respectively different proportions of the unidirectional voltage from the supply circuit, and in fourth and fifth ones of which the voltage received across the winding means corresponds in amplitude with, but has the opposite sign to, that said proportion existing during a respective one of the said second and third settings; and control means operative to control the sequence of the settings of the connection means and the duration of each setting such that the resultant voltage variations across the winding means is approximately sinusoidal in shape.

2. An arrangement according to claim 1, in which the said winding means is one of a set of polyphase-connected primary windings, and including a set of polyphase-connected secondary windings mutually inductively coupled with the primary windings.

3. An arrangement according to claim 1, in which the said winding means is mutually inductively linked with secondary winding means in which is produced a voltage waveform corresponding to the voltage produced across the first-mentioned winding means.

4. An arrangement according to claim 3, in which:

the said first-mentioned winding means is one of a set of polyphase primary windings and the said secondary winding means is one of a set of polyphase secondary windings,

the supply circuit comprises a pair of supply lines;

the switchable connection means comprises a plurality of pairs of switches, one pair for each end of each of the primary windings, one switch of each pair being connected between its associated winding end and one supply line and the other switch of the pair being connected between its associated winding end and the other supply line; and the control means is operative to control the switches whereby the voltage variation across each of the other windings of the set of primary windings corresponds to that across the said one of the primary windings, but the voltage variations across all the windings of each set are mutually phase-displaced from each other.

5. An arrangement according to claim 4, in which each switch is an electronically controllable switching element, and the said control means comprises:

a plurality of two-state circuits each connected to a respective one of the switching elements and arranged whereby to maintain the switching element ON when the two-state circuit is in its first state and to maintain the associated switching element OFF when the two-state circuit is in its second state;

a shift register having a plurality of stages each connected to control the state of respective one of the two-state circuits; and

means connected to activate the stages of the shift register in such order that the two-state circuits cause the switching elements to produce the said voltage variations across the windings.

6. An arrangement according to claim 5, in combination with another similar arrangement, the two sets of secondary windings of the arrangements being connected together to produce a composite output signal, the combination including regulating means connected in common to the shift registers in the control means of the two arrangements and operative to produce an adjustable phase difference between the activation of the stages of the two shift registers whereby to regulate the amplitude of the composite output signal.

7. An arrangement according to claim 6, in which the two sets of secondary windings are connected in series and in which the two sets of primary windings are connected in series. 

1. An electrical inverter arrangement, comprising; electrical winding means; a supply circuit energizable to produce a unidirectional voltage; a plurality of switchable connecting means connected between the winding means and the supply circuit and sequentially settable into a plurality of settings in a first one of which the winding means is disconnected from the supply circuit, in second and third ones of which the winding means is connected to the supply circuit but such as to receive respectively different proportions of the unidirectional voltage from the supply circuit, and in fourth and fifth ones of which the voltage received across the winding means corresponds in amplitude with, but has the opposite sign to, that said proportion existing during a respective one of the said second and third settings; and control means operative to control the sequence of the settings of the connection means and the duration of each setting such that the resultant voltage variations across the winding means is approximately sinusoidal in shape.
 2. An arrangement according to claim 1, in which the said winding means is one of a set of polyphase-connected primary windings, and including a set of polyphase-connected secondary windings mutually inductively coupled with the primary windings.
 3. An arrangement according to claim 1, in which the said winding means is mutually inductively linked with secondary winding means in which is produced a voltage waveform corresponDing to the voltage produced across the first-mentioned winding means.
 4. An arrangement according to claim 3, in which: the said first-mentioned winding means is one of a set of polyphase primary windings and the said secondary winding means is one of a set of polyphase secondary windings, the supply circuit comprises a pair of supply lines; the switchable connection means comprises a plurality of pairs of switches, one pair for each end of each of the primary windings, one switch of each pair being connected between its associated winding end and one supply line and the other switch of the pair being connected between its associated winding end and the other supply line; and the control means is operative to control the switches whereby the voltage variation across each of the other windings of the set of primary windings corresponds to that across the said one of the primary windings, but the voltage variations across all the windings of each set are mutually phase-displaced from each other.
 5. An arrangement according to claim 4, in which each switch is an electronically controllable switching element, and the said control means comprises: a plurality of two-state circuits each connected to a respective one of the switching elements and arranged whereby to maintain the switching element ON when the two-state circuit is in its first state and to maintain the associated switching element OFF when the two-state circuit is in its second state; a shift register having a plurality of stages each connected to control the state of respective one of the two-state circuits; and means connected to activate the stages of the shift register in such order that the two-state circuits cause the switching elements to produce the said voltage variations across the windings.
 6. An arrangement according to claim 5, in combination with another similar arrangement, the two sets of secondary windings of the arrangements being connected together to produce a composite output signal, the combination including regulating means connected in common to the shift registers in the control means of the two arrangements and operative to produce an adjustable phase difference between the activation of the stages of the two shift registers whereby to regulate the amplitude of the composite output signal.
 7. An arrangement according to claim 6, in which the two sets of secondary windings are connected in series and in which the two sets of primary windings are connected in series. 